1. Field of the Invention
The present invention relates to a welding wire having an excellent zinc primer resistant performance and good low temperature impact toughness, and more particularly, to a metal cored wire for gas-shielded arc welding having an excellent zinc primer resistant performance and low temperature impact toughness capable of restraining a welding defect due to the welding fume generated by a zinc primer upon welding a steel workpiece on which the zinc primer is coated with for preventing an occurrence of corrosion, enhancing the low temperature impact toughness in the weld metal.
2. Description of the Related Art
Steel materials widely used in a large-scale architecture such as shipbuilding, bridges, steel frames, etc., are large in shape and thickness, and have various shapes. To this end, there frequently occur circumstances that it is impossible to perform a mass production of zinc plated steels through a plating process such as an electric zinc plating or a hot dip galvanizing, etc. Especially, since much time is spent in fabricating such the architectures, it is noted to prevent an occurrence of corrosion.
Accordingly, an inorganic zinc primer containing zinc powder having an excellent corrosion-preventive capability is coated in a thickness range of 10 xcexcm to 100 xcexcm on the surface of the steel material, which prevents a corrosion that may occur at the surface of the steel material during the manufacture of such architectures.
There are various welding methods for welding a steel material on which a zinc primer is deposited. For example, in these days, a gas shielded arc welding method is mainly used for high efficiency of the welding works. The gas shielded arc welding method employs a flux cored wire as a welding consumable and is obtaining the popularity because of various advantages such as good welding workability and arc stability, small occurrence amount of a spatter, and uniform appearance of the welding bead.
However, when a flux cored wire is used in a steel material on which a zinc primer is deposited, a vaporized zinc gas which is generated by a vaporization of zinc powder contained in the primer generates a defect such as a pit or a blow hole at the weld metal. Especially, such defects in the weld metal causes a drawback rendering physical properties to be more worse in an architecture such as shipbuilding or bridge where a low temperature impact characteristic is important.
In order to resolve the aforementioned problems, there are provided a method in which a sufficient deoxidizing alloying agent is added in a filling flux of the flux cored wire and a method in which a filling flux in a lime system is used.
The aforementioned methods, however, contain a lot of basic components in the filling flux and thereby they render the slag covering properties or the bead shape to be worse or the spatter to be excessively generated. Also, these methods lower the ductility of the bead to thereby degenerate the low temperature impact toughness.
Accordingly, an object of the present invention is to provide a metal flux cored wire (hereinafter referred to as metal cored wire) capable of preventing an occurrence of a defect in the weld metal by optimizing a nature of a welding slag and rapidly discharging a welding gas generated during welding and a welding fume into the outside of the weld metal.
Another object of the present invention is to provide a metal cored wire capable of enhancing the low temperature toughness by controlling an amount of a diffusible hydrogen remaining in the weld metal.
Still another object of the present invention is to provide a metal cored wire capable of obtaining a good welding workability.
Additional features and advantages of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the followings or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained as particularly pointed out in the appended claims.
To achieve the object and in accordance with the purpose of the present invention, as embodied and broadly described, a flux cored wire for gas-shielded arc welding comprises a flux filled in a mild steel sheath in an amount of 10% to 25% by weight of the wire. The flux comprises: an oxide of TiO2+SiO2+Al2O3 in an amount of 2% to 10% by weight of the wire; at least one component in an amount of 0.1% to 1.0% by weight of the wire, the one component being selected from a metal fluoride group consisting of CaF2, NaF, K2SiF6, Na2SiF6 and KF, a metal titanium in an amount of 0.1% to 0.25 t % by weight of the wire; a metal boron in an amount of 0.002% to 0.008% by weight of the wire; and a subsidiary component in an amount of 5% to 20% by weight of the wire, the subsidiary component consisting of an iron component, a deoxidizer and an arc stabilizer.